How to Start Unit Testing to a JavaScript Code?

Unit testing is a crucial part of software development that helps ensure individual parts of the code work correctly. For JavaScript, unit testing can be especially valuable given the dynamic nature of the language. This guide will introduce you to the two popular approaches to unit testing in JavaScript providing the descriptions, syntax, and example implementation code.

These are the following approaches:

Using Jest

The Jest is a widely used testing framework developed by Facebook. It is popular for testing React applications but can be used for any JavaScript project. Jest is known for its ease of use, powerful features, and comprehensive documentation.

Syntax:

test('description of the test', () => { 
     // arrange
    // act 
   // assert
});

Let's consider a simple function that adds two numbers and we will write a unit test for it using Jest.

Function Code:

// math.js
function add(a, b) {
  return a + b;
}
module.exports = add;

Test Code:
// math.test.js
const add = require('./math');
test('adds 1 + 2 to equal 3', () => {
     expect(add(1, 2)).toBe(3);
});

Running the Tests: To run the tests, you need to the have Jest installed. We can install it using npm.

npm install --save-dev jest

Then, add a script to your package.json to the run Jest:

"scripts": {   "test": "jest"}

Now you can run your tests using:

npm test

Using Mocha and Chai

Mocha is a feature-rich JavaScript test framework running on the Node.js and in the browser making the asynchronous testing simple and fun. The Chai is an assertion library that pairs well with any JavaScript testing framework. Together, Mocha and Chai provide a powerful and flexible testing environment.

Syntax:

Basic syntax for a Mocha test using the Chai:

const { expect } = require('chai');
describe('description of the test suite', () => 
     {  it('description of the test', () =>
        {   
              // arrange    // act    // assert 
        }
  );
});

Implementation Code: We will use the same function add and write a unit test for it using the Mocha and Chai.

Function Code:

// math.js
function add(a, b) {
  return a + b;
}
module.exports = add;
Test Code:
// math.test.js
const add = require('./math');
const { expect } = require('chai');
describe('Addition function', () => {
    it('should add 1 and 2 to get 3', () => {
      expect(add(1, 2)).to.equal(3);
   });
});

Running the Tests:

To run the tests we need to the have Mocha and Chai installed. we can install them using npm:

npm install --save-dev mocha chai

Then, add a script to your package.json to run Mocha:

"scripts": {  "test": "mocha"}

Now you can run your tests using:

npm test

Conclusion

Unit testing is an essential practice for the maintaining robust and reliable JavaScript code. The Jest and Mocha are two powerful tools that can help you get started with the unit testing. The Jest offers an all-in-one solution with the straightforward setup while Mocha and Chai provide the flexibility and wide range of features. Choose the one that best fits your project's needs and start writing tests to the ensure your code works as expected.